Twitter etiquette isn't only about what you should do. Unfortunately, bad Tweets and poor Twitter practices sometimes show up within microblogging communications. Although you can't really go horribly wrong on Twitter, you'll make your life easier in the Twitterverse if you follow these guidelines:
When you first sign up and before you start tweeting regularly, don't follow hundreds of people. If you follow someone, she checks out your profile to see whether she wants to follow you back; if she sees that you've tweeted once or twice and you're following hundreds of people, she may think you're just a spam account.
Start slowly, following people you know and who know you. Then, as you start tweeting regularly, follow more people based on your interests.
Avoid using punctuation in your username. Typing punctuation on mobile devices is difficult.
Don't share information that you might regret making public.
Don't send an update when a direct message is more appropriate — when the update is meaningless to anyone except one person, for example. If the person doesn't follow you, you can send an update that contains her name, asking her to contact you over another medium.
Don't feel the need to thank everyone publicly for following you. It's a nice thing to do, but not always necessary, and some users even find it irksome.
Don't think that Twitter success has anything to do with your follower count.